We report the first observation of localized modulation of turbulent density fluctuations $\tilde{n}$ (via beam emission spectroscopy) by neoclassical tearing modes (NTMs) in the core of the DIII-D tokamak. NTMs are important as they often lead to severe degradation of plasma confinement and disruptions in high-confinement fusion experiments. Magnetic islands associated with NTMs significantly modify the profiles and turbulence drives. In this experiment $\tilde{n}$ was found to be modulated by 14% across the island. Gyrokinetic simulations suggest that $\tilde{n}$ could be dominantly driven by the ion temperature gradient instability.

• Received 10 December 2015

DOI:https://doi.org/10.1103/PhysRevLett.116.215001